Merge branch 'application-record-where-exists' into 'master'

Add ApplicationRecord.where_exists

See merge request gitlab-org/gitlab!45041

app/models/application_record.rb

@@ -61,4 +61,8 @@ class ApplicationRecord < ActiveRecord::Base
   def self.underscore
     Gitlab::SafeRequestStore.fetch("model:#{self}:underscore") { self.to_s.underscore }
   end
+
+  def self.where_exists(query)
+    where('EXISTS (?)', query.select(1))
+  end
 end

spec/models/application_record_spec.rb

@@ -90,4 +90,12 @@ RSpec.describe ApplicationRecord do
       expect(User.at_most(2).count).to eq(2)
     end
   end
+
+  describe '.where_exists' do
+    it 'produces a WHERE EXISTS query' do
+      user = create(:user)
+
+      expect(User.where_exists(User.limit(1))).to eq([user])
+    end
+  end
 end